The brain drain is real. There is a network of previously unrecognised vessels that rid the brain of unwanted extracellular fluids and other substances, including amyloid-beta – a peptide that accumulates in the brain of people with Alzheimer’s. The new discovery looks set to add to our understanding of the disease.

Jeffrey Iliff at the University of Rochester Medical Centre, New York, and his colleagues, were intrigued by the fact that there are no obvious lymphatic vessels in the brain. Among other things, the lymphatic system removes waste interstitial fluids from body tissue.

“It seemed strange that such an important and active organ wouldn’t have a specialised waste-removal system,” says Iliff.

When the researchers added fluorescent and radioactive tracers to the cerebrospinal fluid of live mice, the tracers quickly spread throughout the rodents’ brains. Using two-photon microscopy to visualise the movement in real-time, the team saw cerebrospinal fluid permeating the entire brain through ‘pipes’ surrounding blood vessels, similar to the lymphatic system that services all other organs.